The concept of drawing and supplying energy between a battery and a power grid is known. Such a concept when applied to a vehicle battery and power grid is commonly referred to as vehicle to grid/grid to vehicle (V2G/G2V). The vehicle battery draws power as needed and supplies power during times when the battery has a surplus of power. For instance, at certain periods, also referred to as peak periods, of the day the load demand placed upon the grid may strain the supply available. In such instances, the grid requires auxiliary power sources to meet the excess demand. As a result, power supplied by the grid during these times is often sold at a premium price, also referred to as a peak-rate. “Peak-rate” as used herein refers to the price of power when the power source must obtain auxiliary power to meet the load demand. The peak-rate is often more costly than other times as the power source has to pay for additional power to meet the power demand. In other periods of the day the power demand is well below the power available and thus power supplied during these “off-peak” periods is often sold at a reduced rate. With the popularity and dissemination of what is commonly referred to as plug-in electric vehicles, power sources such as commercial grids will have a potentially large source of power to tap into during peak times.
Naturally, the power source also charges the batteries. Accordingly, it may be advantageous for users of plug-in vehicles to only charge their batteries during off-peak times so as to minimize their vehicle's operating costs. However, there may be instances where the user would rather pay a premium peak rate to charge their battery.
With reference to FIGS. 2A and 2B, a graph showing the general demand cycle of a power source such as a utility grid in a 24-hour period is provided. The period during which most vehicles are not being used and are available for charging, i.e. in the middle of the day and generally at night, provides two different rates. Charging the vehicle in the middle of the day may coincide with peak times, thus the user may pay a premium price. Conversely the user may pay a bargain price for charging the vehicle during off-peak hours, such as at night. Further, the power source may provide premium credit for drawing power from a battery during the day as opposed to at night when power demand is well below the power source's capacity. Accordingly, it remains desirable to have a battery optimization system which generates a charging/discharging cycle that takes advantage of the lower rates provided during off-peak times.
Many users drive their vehicles for extended periods of time twice a day, the first period going to work and the second period coming home from work. The drive may consume such a large amount of power from the battery that it is necessary for the driver to charge the battery while at work and again at night. However, in some instances only one full charge is needed to support the drive to and from work. Thus, it may be advantageous from a cost perspective to fully charge the battery at night and partially during the day.
With reference now to FIG. 3, a chart showing the life of a vehicle battery with respect to the depth of discharge is provided. As shown, a daily deep discharge and recharge cycle can significantly shorten the life of the battery. However, small discharges and recharges will extend the life of the battery. Furthermore, each battery has its own optimal charging/discharging cycle for extending the life of the battery. For instance some batteries require a full discharge prior to recharging the battery in order to optimize the life of the battery while other batteries will optimize their life when small depth discharges and recharges occur.
“Charging/discharging cycle” as used herein refers to the depth and rate of the charge and discharge of power from the battery. Thus certain battery usage may be optimal for charging and discharging the battery so as to extend the life of the battery while other usage patterns will shorten the life of the battery as the charge and discharge from the battery is not in accordance with the battery's optimal charging/discharging cycle.
The optimal charging/discharging cycle may be affected by the material used to make the battery, the usage of the battery, the temperature in which the battery operates, and the like. For instance, it is known that the optimal charging/discharging cycle of a Nickel Metal Hydride Battery is different from that of a Lithium Ion Battery. In some instances it may not be practical to charge the battery in accordance with a charging/discharging cycle that maximizes the life of the battery. For instance, the battery's power may be low and the user may only have a relatively short period of time to charge the battery. In such a case the user may opt to forego charging the battery at a charging/discharging cycle that is optimal to extend the life of the battery and rather charge the battery at a charging/discharging cycle that draws as much power as possible in as short a time as possible. In other instances the user may be more cost conscious and thus only desire to charge the battery during times when the power source rate is at a low and may only desire to supply power to the power source at the highest rate of return.
Accordingly it remains desirable to have a battery optimization system operable to calculate an optimal charging/discharging cycle of a battery so as to achieve the end goal of the user. Such a battery optimization system allows for dynamic optimization of battery use that meets the changing preferences of the end user. For instance, the user may base the charging/discharging cycle upon either the desire to extend the life of the battery as long as possible, reduce the cost of operating and maintaining the battery, or to have the battery at full capacity in as short a time as possible. Furthermore, the battery optimization system may calculate an optimal charging/discharging cycle based not only upon user preference, but the state of the battery, and the power source.